(Updated) Arrest made in hit-and-run on Massachusetts Avenue

Police are investigating a pedestrian hit-and-run in Back Bay at about 6 a.m. Wednesday.

Update: At about 2:50 p.m. Boston police said they arrested 69-year-old Lawrence Stead of Quincy and charged him with leaving the scene of an accident causing personal injury. He will be arraigned in court on Thursday.

Cambridge police said that Stead was an officer with that city's department for more than 25 years. He retired in 2009.

Original story is below:

A person is being treated for life-threatening injuries after being run down by the driver of a car that failed to stop near the Massachusetts Avenue MBTA station Wednesday morning.

As of 11 a.m., police are continuing their search for the hit-and-run driver.

Boston police said that the car believed to be involved in the crash was located. Police did not say exactly where the car was located, but according to WCVB, the 1999 Mercury Grand Marquis was found by police in Quincy.

Emergency crews were called to the area of the Massachusetts Avenue T stop at about 6 a.m. for the crash, according to Boston police. Investigators closed down part of the busy roadway for hours while they collected evidence at the scene, which was near a crosswalk. The victim was taken to Boston Medical Center.